# !!! warning "Experimental implementation (upwind SBP)"
#     This is an experimental feature and may change in future releases.

using OrdinaryDiffEqSSPRK
using Trixi

###############################################################################
# semidiscretization of the compressible Euler equations

equations = CompressibleEulerEquations3D(1.4)

"""
    initial_condition_taylor_green_vortex(x, t, equations::CompressibleEulerEquations3D)

The classical inviscid Taylor-Green vortex.
"""
function initial_condition_taylor_green_vortex(x, t,
                                               equations::CompressibleEulerEquations3D)
    A = 1.0 # magnitude of speed
    Ms = 0.1 # maximum Mach number

    rho = 1.0
    v1 = A * sin(x[1]) * cos(x[2]) * cos(x[3])
    v2 = -A * cos(x[1]) * sin(x[2]) * cos(x[3])
    v3 = 0.0
    p = (A / Ms)^2 * rho / equations.gamma # scaling to get Ms
    p = p +
        1.0 / 16.0 * A^2 * rho *
        (cos(2 * x[1]) * cos(2 * x[3]) + 2 * cos(2 * x[2]) + 2 * cos(2 * x[1]) +
         cos(2 * x[2]) * cos(2 * x[3]))

    return prim2cons(SVector(rho, v1, v2, v3, p), equations)
end
initial_condition = initial_condition_taylor_green_vortex

D_upw = upwind_operators(SummationByPartsOperators.Mattsson2017,
                         derivative_order = 1,
                         accuracy_order = 4,
                         xmin = -1.0, xmax = 1.0,
                         N = 16)
flux_splitting = splitting_steger_warming
solver = FDSBP(D_upw,
               surface_integral = SurfaceIntegralUpwind(flux_splitting),
               volume_integral = VolumeIntegralUpwind(flux_splitting))

coordinates_min = (-1.0, -1.0, -1.0) .* pi
coordinates_max = (1.0, 1.0, 1.0) .* pi
mesh = TreeMesh(coordinates_min, coordinates_max,
                initial_refinement_level = 2,
                periodicity = true)

semi = SemidiscretizationHyperbolic(mesh, equations, initial_condition, solver;
                                    boundary_conditions = boundary_condition_periodic)

###############################################################################
# ODE solvers, callbacks etc.

tspan = (0.0, 10.0)
ode = semidiscretize(semi, tspan)

summary_callback = SummaryCallback()

analysis_interval = 100
analysis_callback = AnalysisCallback(semi, interval = analysis_interval,
                                     save_analysis = true,
                                     extra_analysis_integrals = (energy_total,
                                                                 energy_kinetic,
                                                                 energy_internal))

alive_callback = AliveCallback(analysis_interval = analysis_interval)

save_solution = SaveSolutionCallback(interval = 1000,
                                     save_initial_solution = true,
                                     save_final_solution = true,
                                     solution_variables = cons2prim)

callbacks = CallbackSet(summary_callback,
                        analysis_callback,
                        alive_callback,
                        save_solution)

###############################################################################
# run the simulation

sol = solve(ode, SSPRK43(); abstol = 1.0e-6, reltol = 1.0e-6,
            ode_default_options()..., callback = callbacks)
